1. Field
Various embodiments relate to optical fibers such as, for example, optical fibers with large core dimensions, optical fibers that support single mode propagation, and multi-core fibers, as well as their use as optical amplifiers or lasers.
2. Description of the Related Art
Single mode optical fibers provide a flexible delivery medium for high quality optical beams. Conventional single mode fibers typically have a core diameter below 9 μm. However, the small core diameter of conventional single mode fiber is not well suited for delivery of high power optical beams. High optical intensity beams propagating in these fibers can cause strong nonlinear effects such as self-phase modulation, Raman scattering, Brillouin scattering, etc. Self-phase modulation can lead to pulse distortions. Raman and Brillouin scattering can lead to significant power loss during transmission.
Recently, fiber amplifiers and lasers based on rare-earth ions have found advantages in many applications over their solid state counterparts and their power level has been improving. However, in applications requiring high pulse energies and high peak pulse powers, fiber amplifiers still lag their solid-state counterparts because of the small mode area of optical fibers leading to significant nonlinear pulse distortions and optical damage at high peak powers, whereas mode sizes in solid-state amplifier materials can be scaled indefinitely, only limited by thermal considerations or material growth limitations.
The upper peak power limit for fiber lasers may be extended with designs using a large core diameter. Indeed many approaches have been suggested for increasing the fundamental mode area of optical fibers, based for example and not limited to fundamental mode propagation in multi-mode fibers (U.S. Pat. No. 5,818,630), photonic crystal or micro-structured fibers (U.S. Pat. No. 7,289,709), leakage channel or holey fibers (U.S. Pat. No. 7,280,730, U.S. Patent Application Pub. No. 2009/0123121, and International Pub. No. WO 2009/042347, which is incorporated by reference herein for the material specifically referred to herein and for all other material that it discloses) and gain-guided or anti-guided fibers (U.S. Pat. Nos. 5,818,630, 6,751,388, and U.S. Patent Application Pub. No. 2008/0198879) as well as stress guided fibers (International Pub. No. WO 2009/042347, which is incorporated by reference herein for the material specifically referred to herein and for all other material that it discloses). Examples of coherent addition of multi-core fibers have been described for fiber mode area scaling in “High Power Parallel Fiber Arrays”, published as U.S. Patent Application Pub. No. 2009/0201575.
In a system described in U.S. Pat. No. 6,904,219 (to Fermann), Fermann described embodiments of a planar waveguide with conventional waveguiding in the small axis and a thermal lens in the long axis.
High power fiber amplifiers and lasers can be cladding pumped as, for example, embodiments described in U.S. Pat. Nos. 4,815,079 and 5,818,630. However, it has also been realized in U.S. Pat. No. 5,847,863 to Galvanauskas et al. that embodiments of high power fiber amplifiers and lasers can be directly core-pumped using another high power fiber laser, where the fiber pump laser can then be conveniently cladding pumped. Both the pump source and the amplifier can be based on the same rare earth gain medium. The concept has recently been extended with the use of highly doped Yb fibers as pump sources as well as amplifier sources (e.g., U.S. patent application Ser. No. 12/630,550, which is incorporated by reference herein for the material specifically referred to herein and for all other material that it discloses).